Tunable Optical Assembly With Vibration Dampening

ABSTRACT

An optical assembly is formed by one or more piezoelectric fiber composite actuators having one or more optical fibers coupled thereto. The optical fiber(s) experiences strain when actuation voltage is applied to the actuator(s). Light passing through the optical fiber(s) is wavelength tuned by adjusting the actuation voltage.

ORIGIN OF THE INVENTION

This invention was made by employees of the United States Government andmay be manufactured and used by or for the Government of the UnitedStates of America for governmental purposes without the payment of anyroyalties thereon or therefor. Pursuant to 35 U.S.C. § 119, the benefitof priority from provisional application 60/729,048, with a filing dateof Oct. 21, 2005, is claimed for this non-provisional application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to optical fiber tuning. More specifically, theinvention is an optical assembly that can be used to tune an opticalfiber while also providing vibration dampening therefor.

2. Description of the Related Art

Strain tuning of optical fibers is known in the art and is currentlyaccomplished in a variety of ways to include the use of piezoelectricand magnetic actuating elements. In terms of piezoelectric actuatingelements, a stack of piezoelectric elements is typically required inorder to provide the needed amount of mechanical movement because, ingeneral, piezoelectric materials are not capable of producing largeamounts of mechanical displacement upon actuation. Thus, the requirementthat a stack of piezoelectric elements be used adds to the weight of anoptical fiber tuning system. See, for example, U.S. Pat. No. 6,240,220.In terms of magnetic actuating elements, a multiplicity of magnets areused to stretch tune an optical fiber. See, for example, U.S. Pat. No.5,999,546. However, the magnets are relatively heavy and bulky, and canbe adversely affected by environmentally-present magnetic fields.

The stretch or compression (i.e., strain) tuning of an optical fiber iscritical for a tunable fiber laser. In these types of lasers, an opticalfiber having one or more Bragg gratings is strain tuned to provide adesired lasing wavelength. However, the Bragg gratings are sensitive tovibrations so that a tuning mechanism should also ideally providevibration dampening for an optical fiber's Bragg gratings.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anoptical assembly that can strain tune an optical fiber.

Another object of the present invention is to provide a lightweightoptical assembly that can be used to strain tune an optical fiber.

Still another object of the present invention is to provide an opticalassembly that can be used to strain tune an optical fiber and providevibration dampening therefor.

Other objects and advantages of the present invention will become moreobvious hereinafter in the specification and drawings.

In accordance with the present invention, an optical assembly has atleast one piezoelectric fiber composite actuator adapted to have anactuation voltage applied thereto and has at least one optical fibercoupled to the actuator. The optical fiber experiences strain when theactuation voltage is applied to the actuator. A voltage source can beprovided to apply the actuation voltage. Light passing through theoptical fiber is wavelength tuned by adjusting the actuation voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an optical assembly using onepiezoelectric fiber composite actuator in accordance with an embodimentof the present invention;

FIG. 2 is a schematic cross-sectional view of the optical assembly shownin FIG. 1;

FIG. 3 is a schematic cross-sectional view of the optical assembly as itincorporates a plurality of optical fibers;

FIG. 4 is a schematic view of an optical assembly using twopiezoelectric fiber composite actuators in accordance with anotherembodiment of the present invention;

FIG. 5 is a schematic cross-sectional view of the optical assembly shownin FIG. 4;

FIG. 6 is a schematic view of an optical assembly using threepiezoelectric fiber composite actuators in accordance with anotherembodiment of the present invention;

FIG. 7 is a schematic view of the optical assembly embodiment of FIG. 4coupled to a voltage source for applying an actuation voltage to each ofthe assembly's actuators; and

FIG. 8 is a schematic view of the optical assembly embodiment of FIG. 6further having a light source coupled to one end of the optical fiber.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and more particularly to FIG. 1, anoptical assembly that provides for the strain tuning of an optical fiber12 is illustrated schematically and is referenced generally by numeral10. Where incorporated into optical assembly 10, optical fiber 12 caninclude one or more Bragg gratings 14 as would be the case, for example,when optical assembly 10 forms a portion of a fiber laser as will beexplained further below. In terms of optical assembly 10, optical fiber12 is at least partially embedded in and coupled to a piezoelectricfiber composite actuator 16.

Actuator 16 is any conventional piezoelectric fiber composite actuatorhaving the following structural features:

(i) a layer of individual piezoelectric fibers (e.g., round, square,etc.) arrayed side-by-side and typically encased in a polymer matrixmaterial;

(ii) interdigitated electrodes etched or deposited onto one or two(e.g., usually two as will be described in the illustrated examples)polymer film layers with the resulting layers sandwiching the layer ofpiezoelectric fibers.

The layer of individual piezoelectric fibers can be assembled fromindividually-extruded piezoelectric fibers or can be formed from a macrosheet of polymer-backed piezoelectric material that has been processed(e.g., the piezoelectric material has been mechanically diced or etched,laser etched, etc.) to yield parallel rows of piezoelectric material“fibers” attached to the polymer backing. A piezoelectric fibercomposite actuator constructed in this fashion is known as a macro-fibercomposite actuator. A more complete description of such an actuator isdisclosed in U.S. Pat. No. 6,629,341, the contents of which are herebyincorporated by reference.

The above-described structure of optical assembly 10 is also illustratedin a schematic cross-section in FIG. 2 where interdigitated electrodelayers 16A and 16B are sandwiched about and coupled to a piezoelectricfiber layer 16C with optical fiber 12 essentially replacing one of thepiezoelectric fibers comprising layer 16C. It is to be understood thatpiezoelectric fiber layer 16C can be realized by eitherindividually-extruded fibers or piezoelectric “fibers” formed from amacro-sheet of piezoelectric material as would be the case in amacro-fiber composite actuator. The present invention is further notlimited to the use of a single optical fiber, as multiple optical fibers12 could be embedded in piezoelectric fiber layer 16C as shown in FIG.3.

In operation, an actuation voltage is applied to the interdigitatedelectrodes (not shown) in layers 16A and 16B. The applied voltagestrains layer 16C which, in turn, strains layers 16A and 16B that arecoupled to layer 16C. The applied voltage is controlled in order tocontrol the strain in layer 16C and, therefore, the strain tuning ofoptical fiber 12 incorporated into layer 16C. That is, since opticalfiber 12 is also coupled to layers 16A and 16B, optical fiber 12 willexperience the strain along with the piezoelectric fibers comprisinglayer 16C. Further, since optical fiber 12 (and any Bragg gratingsformed thereon) are embedded within actuator 16, the resulting opticalassembly 10 is a construction that also provides vibration dampening foroptical fiber 12.

Another embodiment of the present invention is illustrated in FIGS. 4and 5 where an optical assembly 20 uses two piezoelectric fibercomposite actuators 16. Each of actuators 16 can be constructed asdetailed previously herein. That is, in optical assembly 20, each ofactuators 16 is a finished or complete actuator with actuators 16sandwiching/encasing a region of optical fiber 12 which, as in theprevious embodiments, can include Bragg gratings 14. The structure ofoptical assembly 20 can be accomplished by applying an adhesive bond tothe various elements and then curing the assembly in a vacuum bag in anautoclave oven. However, it is to be understood that other bondingtechniques could also be used without departing from the scope of thepresent invention. Similar to the embodiment shown in FIG. 3, thistwo-actuator construction could also be adapted for use with amultiplicity of optical fibers.

Optical assembly 20 can be operated to apply strain evenly to opticalfiber 12 when each actuator 16 imparts the same strain thereto. However,optical assembly 20 could also be operated to apply a differentialstrain to optical fiber 12 (i.e., to bend optical fiber 12) inaccordance with different actuation voltages being applied to actuators16. Thus, it is to he understood that the present invention is notlimited by the various operational requirements that might be placed onoptical assembly 20.

Still another embodiment of the present invention is illustrated in FIG.6 where an optical assembly 30 is essentially a combination of theoptical assemblies presented in FIGS. 1 and 4. More specifically,optical assembly 10 is sandwiched between and is coupled to two finishedor complete piezoelectric fiber composite actuators 16. Once again,while only one optical fiber 12 is illustrated, a multiplicity ofoptical fibers can be supported by optical assembly 10. The advantagesof this construction are that more actuator force can be developed tostrain the optical fiber(s), and that vibration dampening is enhanced.

As mentioned above, the actuators used in the various embodiments of thepresent invention are adapted to have an actuation voltage appliedthereto in order to generate strain in the actuator's piezoelectricfibers. Accordingly, each optical assembly of the present inventioncould include a voltage source. For example, optical assembly 20 (FIGS.4 and 5) is illustrated in FIG. 7 with a voltage source 40 coupled toeach actuator 16. Voltage source 40 would typically be a controllablevoltage source for applying the same or different actuation voltages toactuators 16.

The present invention could also form part of an optical assembly thatcould be tuned to output different wavelengths of light (e.g., in theform of a laser beam). For example, the optical assembly in FIG. 8includes optical assembly 20, voltage source 40, and a light source 50(e.g., a laser pump) coupled to optical fiber 12 such that lightgenerated by source 50 is coupled into one end 12A of optical fiber 12.Voltage source 40 applies an actuation voltage to each of actuators 16in order to strain tune optical fiber 12 to control the wavelength of alight beam 100 exiting end 12B of optical fiber 12. It is to beunderstood that either of optical assemblies 10 or 30 could be used inplace of optical assembly 20 in the embodiment shown in FIG. 8.

The advantages of the present invention are numerous. The opticalassembly provides the means to strain tune an optical fiber whilesimultaneously providing vibration dampening for the assembly's opticalfiber(s).

Although the invention has been described relative to a specificembodiment thereof, there are numerous variations and modifications thatwill be readily apparent to those skilled in the art in light of theabove teachings. For example, the structure of the present inventioncould also be used in a sensing application to sense the strain producedby a piezoelectric fiber or macro-fiber composite actuator. Further, thetunable optical element need not be a Bragg grating as other tunableoptical elements such as a Fabry-Perot optical sensor could beincorporated into the optical fiber(s). It is therefore to be understoodthat, within the scope of the appended claims, the invention may bepracticed other than as specifically described.

1. An optical assembly, comprising: at least one piezoelectric fibercomposite actuator adapted to have an actuation voltage applied thereto;and at least one optical fiber coupled to said actuator wherein saidoptical fiber experiences strain when the actuation voltage is appliedto said actuator.
 2. An optical assembly as in claim 1 wherein said atleast one piezoelectric fiber composite actuator is a piezoelectricmacro-fiber composite actuator.
 3. An optical assembly as in claim 1wherein said optical fiber includes at least one tunable optical elementselected from the group consisting of a Bragg grating and a Fabry-Perotoptical sensor.
 4. An optical assembly as in claim 1 wherein saidoptical fiber is embedded within said actuator.
 5. An optical assemblyas in claim 1 wherein said at least one piezoelectric fiber compositeactuator comprises a first piezoelectric fiber composite actuator and asecond piezoelectric fiber composite actuator with said at least oneoptical fiber being positioned between said first actuator and saidsecond actuator.
 6. An optical assembly as in claim 5 wherein said atleast one piezoelectric fiber composite actuator further comprises athird piezoelectric fiber composite actuator with said optical fiberbeing embedded therein and said third actuator being sandwiched betweensaid first actuator and said second actuator.
 7. An optical assembly,comprising: a first piezoelectric macro-fiber composite (PMFC) actuator;a second PMFC actuator; and at least one optical fiber positionedbetween and coupled to said first PMFC actuator and said second PMFCactuator.
 8. An optical assembly as in claim 7 wherein said opticalfiber includes at least one tunable optical element selected from thegroup consisting of a Bragg grating and a Fabry-Perot optical sensor. 9.An optical assembly as in claim 7 further comprising a third PMFCactuator with said optical fiber being embedded therein and said thirdPMFC actuator being sandwiched between said first PMFC actuator and saidsecond PMFC actuator.
 10. An optical assembly, comprising: at least onepiezoelectric fiber composite actuator; at least one optical fibercoupled to said actuator; and a voltage source coupled to said actuatorfor applying an actuation voltage thereto.
 11. An optical assembly as inclaim 10 wherein said at least one piezoelectric fiber compositeactuator is a piezoelectric macro-fiber composite actuator.
 12. Anoptical assembly as in claim 10 wherein said optical fiber includes atleast one tunable optical element selected from the group consisting ofa Bragg grating and a Fabry-Perot optical sensor.
 13. An opticalassembly as in claim 10 wherein said optical fiber is embedded withinsaid actuator.
 14. An optical assembly as in claim 10 wherein said atleast one piezoelectric fiber composite actuator comprises a firstpiezoelectric fiber composite actuator and a second piezoelectric fibercomposite actuator with said at least one optical fiber being positionedbetween said first actuator and said second actuator.
 15. An opticalassembly as in claim 14 wherein said at least one piezoelectric fibercomposite actuator further comprises a third piezoelectric fibercomposite actuator with said optical fiber being embedded therein andsaid third actuator being sandwiched between said first actuator andsaid second actuator.
 16. An optical assembly, comprising: at least onepiezoelectric fiber composite actuator; an optical fiber having a firstend and a second end, said optical fiber having at least one tunableoptical element formed in a region thereof that is coupled to saidactuator, said at least one tunable optical element selected from thegroup consisting of a Bragg grating and a Fabry-Perot optical sensor; avoltage source coupled to said actuator for applying an actuationvoltage thereto; and a light source coupled to said first end of saidoptical fiber.
 17. An optical assembly as in claim 16 wherein said atleast one piezoelectric fiber composite actuator is a piezoelectricmacro-fiber composite actuator.
 18. An optical assembly as in claim 16wherein said optical fiber is embedded within said actuator.
 19. Anoptical assembly as in claim 16 wherein said at least one piezoelectricfiber composite actuator comprises a first piezoelectric fiber compositeactuator and a second piezoelectric fiber composite actuator with saidat least one optical fiber being positioned between said first actuatorand said second actuator.
 20. An optical assembly as in claim 19 whereinsaid at least one piezoelectric fiber composite actuator furthercomprises a third piezoelectric fiber composite actuator with saidoptical fiber being embedded therein and said third actuator beingsandwiched between said first actuator and said second actuator.
 21. Anoptical assembly, comprising: a first piezoelectric macro-fibercomposite (PMFC) actuator; a second PMFC actuator; an optical fiberhaving a first end and a second end, said optical fiber having at leastone tunable optical element formed in a region thereof that ispositioned between and coupled to said first PMFC actuator and saidsecond PMFC actuator, said at least one tunable optical element selectedfrom the group consisting of a Bragg grating and a Fabry-Perot opticalsensor; a voltage source coupled to said first PMFC actuator and saidsecond PMFC actuator for applying an actuation voltage thereto; and alight source coupled to said first end of said optical fiber.
 22. Anoptical assembly as in claim 21 further comprising a third PMFC actuatorwith said region of said optical fiber being embedded therein, saidthird PMFC actuator being sandwiched between said first PMFC actuatorand said second PMFC actuator.